Sacralization of Coccygeal Vertebra: A Descriptive Observational Study in Bangladesh

Background: In the sacrococcygeal region, anatomical variation is due to the sacralization of the coccygeal vertebra, which is the due union of/fusion of the fifth sacral with the first coccygeal vertebra of five couples of sacral foramina under-detected or asymptomatic beyond radiological assessment. That is why it is challenging to know the cause of coccydynia, caudal block failure, the difficult second stage of labor, and perineal tears. The present study aims to improve knowledge about the anatomical variation of sacralization of the coccygeal vertebra. Additionally, to find the prevalence of sacralization of coccygeal vertebra in Sylhet, Bangladesh. Methods: This study was performed on 60 parched, totally calcified, typical sacra of mature-age individuals of undetermined sexes, fulfilling the inclusion criteria from the bone bank of the osteology museum of the Department of Anatomy, Sylhet MAG Osmani Medical College, Sylhet, Bangladesh, from July 2017 to June 2018. Sex determination of the collected unknown sacra was conducted using discriminant function analysis. It was found that 50% (30) were male and 50% (30%) were female. The unpaired t-tests and chi-square were utilized to determine the statistical significance. Results: Out of 60 sacra, eight (13.33%) samples presented with sacralization. This study found that males had significantly higher straight (p=0.05) and curved (p=0.05) lengths of sacrococcygeal vertebrae. The sacrococcygeal curvature index (SCI) showed statistically significant (p=0.05) differences between the sexes. Conclusion: Sacralization may exert an impact on the caudal block. It could extend the second stage of the labor process with perineal tears. Therefore, knowledge about the anatomical variation of the coccygeal vertebra is essential.


Introduction
The typical vertebral column consists of seven cervicals, twelve thoracics, five lumbar, five sacral, and four coccygeal vertebrae, thereby totaling thirty-three [1]. Multiple studies reported that the disparities in the vertebral column occur from the typical configuration [2][3][4]. Furthermore, lumbosacral transitional vertebrae (LSTV) are inborn spinal paradoxes through either sacralization (bottommost lumbar segment) or lumbarization (topmost sacral part) of the vertebral column [5]. LSTV is a frequent but incidental detection among the populace [6], with a reported prevalence of 4-36% [6][7][8]. The sacrum is a considerable triagonal bone positioned at the bottom of the backbone [9,10]. It helps transmit body mass load from the chest and abdomen to the pelvis and lower extremities [9,10]. The sacrum is self-possessed by a union of five vertebrae to configure a wedge-shaped bony cornucopia with four twosomes of sacral openings [10]. The typical sacrum has four pairs of frontward (pelvic) and rearward (dorsal) sacral orifices, which give passage to the sacral canal and corresponding sacral nerves that travel by virtue of these spaces (between sacral bone [SB] 1 and SB2 [S1 space], SB2 and SB3 [S2 space], SB3 and SB4 [S3 space], SB4 and SB5 [S4 space]) [11,12]. The existence of five duos of the sacral opening is an anatomical abnormality formed because of the attachment of an additional vertebra at the crown or rear end of the sacrum [11]. The combination of the fifth lumbar with the first sacral bone resulted in the sacralization of the lumbar vertebrae [10,13]. It is often described as the ossification of the first coccygeal bone with the fifth sacral or the peak of the sacrum, known as the sacralization of the coccygeal vertebra at the caudal end [13]. The reported prevalence of sacralization varies from 4.1-11% [7,14].
The five-pair sacral opening builds as a result of coccygeal sacralization, and the fifth pair of sacral and coccygeal nerves travel through this opening [15]. Sacralization infrequently causes symptoms and may

Clinical implication of sacralization
The sacralization of the coccygeal vertebra often promotes coccydynia, failure of caudal anesthesia, the troublesome and extended second phase of labor, and perineal laceration [9,36]. Patients with a fused coccyx who could not flex while sitting were more likely to experience coccygeal pain than those with a normal coccyx [37,38]. The sacrococcygeal joint has been wiped out by the fusion of the first coccygeal segment with the sacrum [39,40]. It has been reported that there is a strong relationship between sacralization and low back pain (LBP) [13,41,42]. Sacralization is not continually interrelated to LBP; it can remain symptom-free for eras [16,43,44]. The pain due to the sacralization process is usually slow onset. It progressively changes to dreadful, possibly because of compulsion on nerve/nerve trunks, ligamentous strain, compression of soft tissues between bony joints, the concurrent existence of arthritis, or bursitis [33].

Sacralization and Caudal Nerve Block
The sacrum is an indispensable anatomical structure for the caudal epidural block. This anesthetic block is frequently used to diagnose and treat lumbar spine illnesses [45,46]. The caudal anesthetic procedure is frequently required for multiple surgical needs such as herniorrhaphy, surgery of the lower extremities, lower abdominal surgery (cesarean section, prostate surgery), etc. [47]. Sacralization makes it problematic to spot the landmark need for caudal epidural block, leading to caudal block failure [47]. The caudal procedure is also used in pediatric cases for postoperative analgesia [48]. Consequently, there may be insufficient analgesia due to sacral anatomical anomalies [49].

Sacralization and Obstetrics
Usually, the first coccygeal vertebra is mobile and is pushed posteriorly during the second phase of labor [15]. Therefore, the anteroposterior diameter of the pelvis outlet expands and facilitates giving birth [15]. The coccyx becomes fixed when fused with the sacrum [39,50]. Consequently, the anteroposterior outlet diameter does not increase [51,52], which may lead to protracted labor and perineal injuries [53,54]. Sacralization also causes trouble during the instrumental parturition process. Subsequently, evaluating all pregnant women for sacralization is highly recommended to ensure better clinical outcomes [20,55].
Nonetheless, this is a frequently encountered anatomical and clinical anomaly of the sacrum. A few or less number of research studies have been conducted in Bangladesh and several low-and middle-income countries (LMICs; underdeveloped and developing countries). The knowledge of anatomy and anatomical variation [56][57][58] of the sacrococcygeal region is fundamental in many clinical situations, including the most vital issue of normal vaginal childbirth.

Objectives of the study
The current research is intended to determine the anatomical variations (sacralization of the coccygeal vertebra (incidence/prevalence) of the sacrum and coccyx through morphometric assessments among the Bangladeshi community. Therefore, this study possibly helps Bangladeshi populations and other geopolitical arenas effectively treat these anatomical ailments. This study's statistics can be used to compare similar research findings locally and overseas. Hopefully, our data will enhance the database of anatomical variants of the sacrum.

Study Design and Sample Selection
This was a descriptive, non-experimental investigation study. The research samples were collected from the Department of Anatomy, Sylhet MAG Osmani Medical College, Sylhet. Sacra from both men and women were incorporated for this research. The sex was grouped by discriminant function analysis. The sacrum was scrutinized to evaluate its vertebral components, and the number of sacral openings was counted. Nonsacralization was viewed as the sacrum showing 04 pairs of orifices and 05 vertebral sections. Alternatively, sacralization was considered as the sacrum showed 05 pairs of openings and 06 vertebral parts.

Study Period, Sampling Method, and Sample Size
This research was conducted from July 2017 to June 2018. Consecutive opportunity sampling was applied to choose the sacrum, and the sample size was 60.

Data Collection Tool and the Procedure of Data Collection
Measuring tape ( Figure 1) and digital slide calipers ( Figure 2) are the tools used for data collection. Data are collected with the help of digital slide calipers along the mid-line of the sacrum from the middle of the anterosuperior margin of the promontory to the middle of the anteroinferior margin of the last coccygeal vertebra. It was recorded in millimeters, and the curved length of the sacrococcygeal vertebra was recorded using flexible ribbon tape. The current study also determines the sacrococcygeal curvature index (SCI). SCI is assessed through "sacrococcygeal straight length divided by sacrococcygeal curved length × 100" [59].

Results
Among the study sample, 86.67% (fifty-two) of sacra were typical. Only 13.33% (eight) sacra showed sacralization of the coccygeal vertebra. Table 1 shows the sacralization of the coccygeal vertebra. This study revealed that males (8.33%) had a higher prevalence of sacralization than females (5%). Figure 3 shows the frequency distribution of sacralization of the coccygeal vertebra. Figures 4-5 show the sacrum (ventral surface and dorsal surface) with 05 pairs of sacral orifices. There was no statistically significant (p=0.706) correlation between sex and sacralization ( Table 2). Among the present study population, males had statistically significantly longer straight (p=0.05) and curved (p=0.05) lengths of sacrococcygeal vertebrae ( Table 3). In this study, population males possess statistically significantly (p=0.05) higher SCI (

Discussion
The global existence of LSTV has been reported to be 4-36% [60]. The LSTV is comprised of sacralization or lumbarization [5,7]. Sacralization is a congenital vertebral abnormality of the lumbosacral spine that often leads to improper recognition and difficulty spotting a vertebral component [13]. Therefore, changes in the biomechanical anatomy of the vertebral column and related anatomical body constituents lead to important clinical consequences, especially in anesthetic techniques and surgical procedures [5]. Furthermore, multiple studies have reported sacral malformation as high as 50% [61,62]. Anatomic congenital deformity sacralization was written almost ten decades ago [63,64]. In this study, the sacralization of coccygeal vertebra among the Bangladeshi population was 13.33%. Among Indians, Nepalese, and Israel, sacralization was reported as 6-11.1% [36,65], 11.1% [66], and 13.1% [67], respectively [36,[65][66][67]. One more recent Indian study revealed 17.7% of sacralization [68]. Therefore, the current study findings were in the same line as studies conducted in neighboring countries of Bangladesh. There has been stated that no statistically significant variability was observed in the prevalence of sacralization between sex in this study. Nevertheless, there have been significant (p<0.001) and non-significant (p>0.05) differences observed in the earlier surveys among the Turkish and Israeli populations, respectively [68,69]. Consequently, our findings were similar [68] and dissimilar [69] to earlier studies. This study revealed that both straight and curved lengths of sacrococcygeal vertebrae were statistically significantly (p=0.05) higher among males. Similar findings were statistically significant in earlier French [7] and Korean [70] studies. One study was conducted in New Zealand. Similarly, female sacrococcygeal vertebrae are short [3], which promotes coccydynia [71,72]. The word coccydynia was first developed in 1859 by Simpson and is also known as coccygodynia and tailbone pain [37,72]. Later, Foye identified coccygodynia as one of the top reasons for LBP [73,74]. LBP is frequently considered a mysterious disorder as several disease pathologies can cause similar painful conditions. It is often difficult to diagnose the root cause of these disorders [75][76][77]. Multiple studies were conducted on slum dweller women (82%), bank staff (36.6%), and physiotherapists (60%) who suffer from low back pain [78][79][80]. One study revealed that a successful coccygectomy had been performed among a group of 20 patients when these patients were resistant to medical therapy [81]. Consequently, this study advocated that health professionals, especially those involved with the childbirth process, should know that sacralization is vital for proper and quick management of this anatomical derivation. Maternal death and prolonged labor are the third leading causes of maternal mortality in Bangladesh and are responsible for 20% of overall demises amongst females [82][83][84][85]. It has been reported that around 60-75% of childbirths happen to be non-institutional and, on most occasions, without help from trained birth attendants [86,87]. Sacralization in women reduces the pelvic passage [15,29], causing inconsistency with the fetal head and often leading to prolonged or obstructed labor for several days. The pressure generated over the perineal area causes necrosis that leads to genital fistula in several poor obstetrics healthcare centers, especially in LMICs [88]. Perineal injury (53-89%) is an enormously common and predictable difficulty of normal vaginal delivery. Moreover, sacralization potentiates the issue by reducing the pelvic outlet [89,90]. With Bangladesh being an LMIC, it has been reported that perineal laceration is common in the country [91][92][93][94][95][96]. The current study findings are significant because sacralization reduces pelvic outlet and increases maternal morbidity. SCI was statistically significantly higher in the present study. It was similar [97] and dissimilar [3] to earlier studies conducted in Kuwait and New Zealand. One study reported that the SCI was statistically significantly nether among coccydynia cases than in the controls and between sex [59]. It has been reported that Bangladeshi women also have coccydynia cases [81]. Multiple overseas studies revealed that coccydynia is predominantly found among female and obese patients [98][99][100]. Consequently, the present study's findings go along with those of the overseas researchers.

Limitations of this study
This study was cross-sectional research. Thereby containing its inherent limitation that cannot measure appropriate disease frequency, especially for the sporadic disease condition. Cross-sectional research only generates a snapshot of the whole story's total picture, not a video or cinema. Consequently, the study results cannot be generalized to the whole country [101]. Moreover, this single-center study often lacks the scientific consistency or relevant extraneous plausibility required for precise information for extensive utilization of our data [102].

Conclusions
Knowing about the sacralization of coccygeal vertebrae is very important for radiologists, neurologists, anesthesiologists, pediatric surgeons, obstetricians, and orthopedic surgeons to manage clinical situations such as prolonged labor, perineal tears, regional block, and LBP. This study highlights the depth of knowledge about anatomical variation, which is helpful for effectively managing several medical and health needs. Furthermore, radiological assessment before any interventional spinal anesthesia is critical, especially for pregnancy, childbirth, and lower abdominal surgical procedures related to the sacrococcygeal region. Although the study has many limitations, nevertheless, the data generated through this may possibly serve as baseline information for future research. Further studies regarding the sacralization of the coccygeal vertebra of the human dry sacrum involving multiple centers and with a larger sample size are recommended. Critical research is needed for detailed information on this variant. All authors reviewed and approved the final version and have agreed to be accountable for all aspects of the work, including any accuracy or integrity issues. Disclosure: The author declares that they have no financial involvement or affiliation with any organization, association, or entity directly or indirectly with the subject matter or materials presented in this article. This includes honoraria, expert testimony, employment, ownership of stocks or options, patents or grants received or pending, or royalties. Authorship contribution: All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis, and interpretation, or in all these areas; they took part in drafting, revising, or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted, and have decided to be accountable for all aspects of the work. Data availability: The current study data is only available from the principal author for research purposes.